The invention relates to a sorting device for sorting out parts by means of air blasts, the sorting device comprising at least one sorting unit provided with a valve support supporting a plurality of electrically actuated sorting valves which have a 2/2-way functionality, which are supplied with compressed air from a common feed passage and each of which is connected to an individual sorting passage leading to a sorting nozzle, wherein each sorting valve can optionally be switched into an open position connecting the associated sorting passage to the feed passage, thereby causing an air blast to emerge from the associated sorting nozzle, or into a closed position, wherein purging air discharged from the sorting nozzle at a lower flow rate than that of the air blast which can be generated in the open position can be fed into each sorting passage from a purge air passage of the sorting device at least in the closed position of the associated sorting valve for cleaning purposes.
A sorting device of this type, which is known from DE 10 2009 006 654 B3, is used in sorting systems for extracting in a controlled manner out of a flow of individual items individual parts, taking account of certain aspects, by the application of compressed air by means of an air blast. Applications are varied, ranging from the food industry via mining to recycling applications in waste reclamation. EP 0 426 893 A1 describes a possible method for using a sorting device, in which the transparency of the parts to be sorted is used as a sorting criterion.
According to DE 10 2009 006 654 B3, the individual air blasts are generated by means of 2/2-way valves, which can be described as sorting valves, are mounted in large numbers on a valve support and installed into the connection between a common feed passage and individual sorting passages, each of the sorting passages leading to a sorting nozzle from which the air blast is discharged as the need arises. In order to avoid a contamination of the sorting valves and/or the sorting passages even at times of prolonged inactivity of individual sorting valves, each sorting valve of the known sorting device is capable of introducing a purge air flow into the associated sorting passage. The purge air flow results from the arrangement that the sorting valves do not disconnect the common feed passage entirely from the associated sorting passage in the closed position, but let a small amount of compressed air to flow through, which then flows through the adjoining sorting passage to act as purge air. As this functionality requires a relatively complex structure of the sorting valves, the known sorting device is likely to be relatively expensive to produce. Moreover, the flow rate of the purge air can only be adjusted individually for each sorting valve, which affects handling in cases in which, owing to varying sorting applications, varying purge air flow rates are appropriate.
In addition, the applicant is aware internally of unpublished sorting devices in which 3/2-way valves are used as sorting valves; in these, a valve port is connected to a purge air passage providing purge air, so that they let purge air flow through the sorting passage whenever the sorting passage is disconnected from the feed passage providing the compressed air for the air blast. The use of 3/2-way valves involves relatively high costs, especially when the fact that sorting devices usually have to be provided with a very high number of sorting valves is taken into account.